Nitride films are of interest for the passivation of semiconductor devices, hardening of metal surfaces, and stabilization of transition metals. When nitride films are applied to semiconductors, the films may function as electrical insulation, chemical resistance, and/or mechanical protection.
Nitride films are commonly formed on other materials via chemical vapor deposition (CVD) using nitrogen (N.sub.2) gas and/or ammonia gas (NH.sub.3). CVD in the context of this document means any and all chemical forms of deposition from the gas phase. Generally, during the formation of these nitride films, a high energy source is used to break, or crack, the bonds of these gaseous compounds in order to generate nitrogen reactants. These compounds are usually cracked either by using high temperatures, for instance, between 700.degree.-1000.degree. C., or by using plasma or ion beam deposition, where high energy nitrogen ions in the gas phase are projected against a material to be coated or covered. The nitrogen reactants then combine with elements at the surface of the material in order to form the nitride film.
Generally, the aforementioned conventional techniques for forming the nitride films are undesirable in a commercial setting, for example, in the manufacture of integrated circuits. If high temperatures are used to create the nitrogen reactants, then the substrate and/or other materials residing on the substrate, for instance, metals, decompose or are altered undesirably because their melting points are surpassed. As an example, consider a gallium arsenide (GaAs) substrate which decomposes at or above 500.degree. C. Moreover, high energy particles, such as particles projected onto a substrate by plasma or ion beam deposition, create undesirable crystalline defects and/or cavities as the high energy particles bombard the substrate surface.
It has been shown in the art that hydrazine (N.sub.2 H.sub.4) can be used as a nitriding agent with silicon substrates in order to form thin films of silicon nitride (Si.sub.3 N.sub.4). See C. Peden et al., "Summary Abstract: Growth Kinetics of Thermally Nitrided Si(100) by N.sub.2 H.sub.4, "J. Vac. Sci. Technol., vol. A5 (4), pp. 2024-2025, July/August 1987, and also, E. A. Slaughter et al., "N.sub.2 H.sub.4 and NH.sub.3 as Precursors for Silicon Nitride Thin Film Growth," J. Vac. Sci. Technol., vol. A10 (1), pp. 66-68, January/February 1992. In the Peden experiments, nitride films were grown using CVD on a silicon substrate at temperatures below 800.degree. C., particularly, at just above room temperature (greater than 50.degree. C.), and with a substrate pressure of about 1.5.times.10.sup.- Torr. Following hydrazine treatment, the films were heated to 550.degree. C. to remove hydrogen which was incorporated during growth. In the Slaughter experiments, nitride films were grown via CVD on a silicon substrate using hydrazine with a substrate temperature of 23.degree. C. (250.degree. K.) and a substrate pressure of about 2.times.10.sup.-10 Torr.
Although meritorious to an extent, the foregoing low temperature techniques for forming nitride films on silicon are disadvantageous because these processes are performed at ultrahigh vacuum conditions (&gt;&gt;atmospheric pressure=760 Torr), which are not easily realized in commercial applications. Even if realized, the commercial process would be unjustifiably expensive and burdensome, and the ultrahigh vacuum conditions can adversely affect other compounds in and on the substrate near the nitride formation. Furthermore, it should be noted these experiments do not suggest procedures for applying nitride films to metals or other semiconductors.
It has further been shown in the art that hydrazine can be used as a nitriding agent with gallium arsenide (GaAs) substrates in order to form thick films, i.e., substrates, of gallium nitride (GAN). See S. Fujieda et al., "Structure Control of GaN Films Grown on (001) GaAs Substrates by GaAs Surface Pretreatments," Japanese Journal of Applied Physics., Vol. 30, No. 9B, pp. 1665-1667, September 1991. In the Fujieda experiments, a GaN film of about 1000 angstroms was formed from a GaAs substrate at 500, 600, and 620.degree. C. The GaN film was grown using metal-organic-CVD (MOCVD) with hydrazine and trimethylgallium (TMG) as sources. At the start of film growth, hydrazine was only introduced for a pretreatment before the addition of TMG. The hydrazine pressure was set at 2.times.10.sup.-4 Torr.
However, the Fujieda process is undesirable and unacceptable for creating nitride films on GaAs and for commercial applications. The apparent focus of Fujieda was the MOCVD deposition of crystalline gallium nitride onto gallium arsenide using trimethylgallium and hydrazine as sources. A N.sub.2 H.sub.4 pretreatment provided a more appropriate crystalline surface orientation for the MOCVD deposition. The substrate temperatures, i.e., 500, 600, and 620.degree. C., are still too high for the coextensive existence of many metals, substrates, and other materials. In fact, the high temperatures in Fujieda unquestionably adversely affected and decomposed GaAs regions remote from the GaN formation because it is well known in the art that GaAs begins to decompose at about 500.degree. C. Furthermore, undesirable vacuum conditions must be maintained in the Fujieda process. Finally, the Fujieda process does not suggest a procedure for creating nitride films with metals or other semiconductors.
Thus, there is an unaddressed need in the art for processes for creating nitride films on metals and semiconductors at low temperature and at desirable pressures without using high energy particles, such as in plasma or ion beam deposition.